Gas turbine engine exhaust ejector/mixer

ABSTRACT

An ejector/mixer for a gas turbine engine includes an annular wall having upstream end adapted to be fastened to an engine case and a downstream end forming a plurality of lobes. A support member interconnects the lobes, and includes an annular blade located radially inwardly of the bight of the lobes. The lobes extend radially inwardly downstream relative to the annular wall and the support member includes an annular blade and has spaced apart joint surfaces spaced apart to coincide with the joint surfaces of a respective lobes. The spaced-apart joint surfaces of the support member being profiled to mate with the corresponding joint surface of the lobes.

TECHNICAL FIELD

The application relates generally to aircraft gas turbine engines and,more particularly, to aft section of the engine including an ejectormixer.

BACKGROUND OF THE ART

In gas turbine engines, hot high velocity air exits from the turbinethrough the core gas path. The exhaust gases may be constrained by anexhaust case section in the form of a corrugated annular case extensionhaving ejector/mixer lobes. Turbofan engines generally use exhaustmixers in order to increase the mixing of the high and low velocityexhaust gas flows. Turbo-shaft engines may be provided with similardevices sometimes referred to as ejectors. Exhaust mixers/ejectors mayexperience thermal variation and/or radial deflection due to exposure tothe high and low velocity flows. In addition, exhaust ejector/mixers maybe prone to vibrations, which has negative consequences for thesurrounding hardware. As such, it is generally desirable to increase thestiffness or rigidity of the exhaust case. Various configurations ofexhaust ejector/mixers have been proposed to date in order to try toincrease the stiffness or reduce deflection thereof.

However, there remains a need for an improved exhaust ejector/mixer fora gas turbine engine.

SUMMARY

In one aspect, there is provided a gas turbine engine having an enginecasing enclosing a compressor section, a combustor and a turbine sectiondefining a main gas path serially extending therethrough, andcomprising: an exhaust cone disposed downstream of the turbine section;an ejector/mixer cantilevered from an aft end of the engine casing, theejector/mixer at least partially surrounding the exhaust cone such as todefine a portion of the main gas path between an outer surface of theexhaust cone and the ejector/mixer; the ejector/mixer having a pluralityof circumferentially distributed lobes; and a support member connectedto at least a number of the lobes; each of the at least number of lobesformed with a trough presenting a joint surface; the support memberhaving corresponding concave joint surfaces profiled for matinglyengaging the corresponding joint surfaces of the lobes.

In another aspect there is an exhaust ejector/mixer for a gas turbineengine adapted to be mounted to a casing at an exhaust end of the gasturbine engine such as to at least partially surround an exhaust cone,the exhaust ejector/mixer comprising: an annular wall having an upstreamend adapted to be fastened to an engine case and a downstream endforming a plurality of circumferentially distributed lobes; and asupport member disposed towards the downstream end of the annular walland interconnecting at least a number of the lobes, each of the at leastnumber of lobes formed with a trough with an convex bight radiallyinward thereof presenting a joint surface; the support member havingcorresponding concave joint surfaces adapted to be joined to the matingconvex joint surfaces of the lobes.

The exhaust ejector/mixer may be provided for a turbofan engine wherealternating lobes extend alternatively radially outwardly and radiallyinwardly. In the this case the support member is joined to the inwardlyextending members only. For a turbo-shaft engine, the lobes might extendinwardly only, in which case the support member is joined to every lobe.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic cross-sectional view of a turbo-shaft gas turbineengine;

FIG. 2 is a rear isometric view of an exhaust ejector/mixer, having asupport member connected to the ejector/mixer lobes thereof, inaccordance with one embodiment of the present disclosure;

FIG. 3 is an enlarged fragmentary, isometric view of a lobe and supportmember according to FIG. 2;

FIG. 4 is a fragmentary rear isometric view an ejector/mixer, having asupport member connected to the lobes thereof, in accordance withanother embodiment;

FIG. 5 is an enlarged fragmentary, isometric view of a lobe and supportmember according to FIG. 4;

FIG. 6 is a schematic, axial cross section of a portion of theejector/mixer showing the main gas path, and the support member locatedand oriented in the gas path; and

FIG. 7 is a schematic, radial cross section of a portion of theejector/mixer showing the hot main gas path and the induced cool air inthe lobes; and illustrating the relative location of the support member.

DETAILED DESCRIPTION

FIG. 1 illustrates a turbo-shaft gas turbine engine 10 of a typepreferably provided for use in subsonic flight, generally comprising inserial flow communication a compressor section 14 for pressurizing theair, a combustor 16 in which the compressed air is mixed with fuel andignited for generating an annular stream of hot combustion gases, and aturbine section 18 for extracting energy from the combustion gases. Thegas turbine engine 10 includes a core engine casing 20 which enclosesthe turbo machinery of the engine. The main air flow passes through thecore of the engine via a main gas path 26, which is circumscribed by thecore engine casing 20 and allows the flow to circulate through themultistage compressor 14, combustor 16 and turbine section 18 asdescribed above.

At the aft end of the engine 10, an exhaust cone 22 is centered about alongitudinal axis X of the engine 10, the exhaust cone 22 beingconnected to an aft end of the turbine section 18. The exhaust cone 22has an outer surface, which defines an inner wall of the main gas path26 so that the combustion gases flow therearound. An ejector/mixer 30forms the outer wall of the aft end of the main gas path 26. As bestseen in FIG. 2, the ejector/mixer 30 includes an annular wall 34 with aradial fastening ring or flange 32 upstream thereof. The fastening ring32 is adapted to be mechanically fastened to the aft portion 20a(FIG. 1) of the casing 20.

Referring to FIGS. 2 and 3, in further detail, the annular wall 34 ofthe ejector/mixer 30, includes and defines a plurality ofcircumferentially distributed radially inner lobes 36 extending axiallyrearwardly from a front frusto-conical portion of the annular wall 34 toa downstream edge 37, i.e. a trailing edge thereof. The lobes 36 includeside, radially-extending, walls 38 with a bight forming an arcuatetrough 40. The trough 40 presents a convex surface 41 on the radiallyinner or central side of the annular wall 34.

An annular support member includes a blade 42 extending concentricallyabout the longitudinal axis X of the engine 10. In the embodiment shown,the blade 42 comprises an annular longitudinal, flat bar. The blade 42is interrupted only at form-fitting joint areas 44. The joint areas 44are located on the blade 42 to correspond with the convex surfaces 41 ofthe lobes 36. The joint areas 44 are curved so that it complements theconvex surface 41, as shown in FIG. 3. The curved joint area 44 isconcave relative to the convex surface 41 of the lobe 36. The blade 42is spaced radially outwardly and independent from the exhaust cone 22and floats with respect thereto. The blade 42 in one embodiment is athin sheet metal strip capable of being welded to the sheet metalforming the annular wall 34. In the embodiment shown in FIGS. 2 and 3,the thin sheet metal strip is formed into a continuous ring.

As mentioned, the ejector/mixer 30 is solely connected to the engine 10at the aft end 20a of the core engine casing 20, and so, theejector/mixer 30 is effectively cantilevered from the core engine casing20. This cantilevered configuration allows the lobes 36 of the exhaustejector/mixer 30 to vibrate at one or more modes in the engine operatingfrequency range, while remaining relatively stiff. In addition, thethermal variations in the exhaust mixer 32 due to the high and lowvelocity flows through the main gas path 26 may cause axial and radialdisplacements in the ejector/mixer 30, which can accordingly be absorbedby the exhaust ejector/mixer 30. Moreover, the downstream end 37 of theejector/mixer 30, which would otherwise be prone to deflection, isreinforced by the blade 42 which serves to increase the rigidity of theexhaust ejector/mixer 30 and thus inhibit movement at the downstream end37 thereof. By joining all the lobes 36 together with the blade 42, anymovement of the ejector/mixer 30 is reduced, as are the vibrationsthereof. In addition, by providing a blade 42 which is independent ofthe exhaust cone 28, i.e. it is free to move relative thereto such as toabsorb any vibrations or thermal growth mismatches therebetween. Theblade 42 is able to accommodate any axial or radial displacements due tosuch thermal variations. As such, the ejector/mixer 30 provides enhancedrigidity and may accommodate thermal variations, vibrations and otherdisplacements, as required.

Another embodiment is shown in FIGS. 4 and 5. In this case, the blade ismade up of blade segments 142 a, 142 b . . . 142 n. Each segment has alength corresponding to the distance between the center lines of twoadjacent lobes 36. Each end of the segment terminates in a partiallyformed concave curve to complement part of the convex surface 41 of thelobe 36. For instance, as shown in FIG. 5, corresponding ends ofsegments 142 a and 142 b make-up the form fitting joint area 144.

The blade 42, 142 may be located at different axial positions along theconvex surfaces 41 of the lobe 36. FIG. 3 illustrates a blade 42 beingspaced upstream from the trailing edge 37, of the lobe 36. As shown inFIG. 5, the blade 142 is located at or slightly downstream from thetrailing edge 37, of the lobe 36. The blade 42, 142 may be fixed to theconvex surfaces 41 of the lobes 36 at joint areas 44, 144 using acombination of resistance, fusion or ball tack welding with a brazingapplication, or other types of suitable bonding that are well known inthe art.

The injector/mixer 30, in the present embodiment, acts to induce coolair, exterior of the engine casing 20, to be drawn radially inwardlythrough the lobes 36 to cool the mechanical parts of the injector/mixer30. As previously mentioned, the support member is often, according tothe prior art, subject to thermal stresses caused by the entrained coolair and of the hot air exiting the turbine 18. FIGS. 6 and 7 show thegases flow in the ejector/mixer 30. The blade 42, 142 is disposeddirectly in the main gas path 26 and is shaped to be laminar with theflow of the hot gases, as can be seen in both FIGS. 6 and 7. The blade42 is essentially exposed only to the hot gases flowing in the main gaspath 26. This reduces the thermal gradient in the blade 42, 142.

The embodiments described show a turbo-shaft engine. However, in thecase of a turbofan engine, cool air from the fan is directed to theejector/mixer 30 which in such a case would have inner and outeralternating lobes to best mix the hot gases with the cool air. U.S. Pat.No. 5,265,807 Steckbeck et al 1993; U.S. Pat. No. 7,677,026 Conete et al2010; and U.S. Pat. No. 8,739,513 Lefebvre et al 2014 describe exhaustmixers which are herewith incorporated by reference.

The above described embodiments provides an improved exhaustejector/mixer for a gas turbine engine where the thermal stresses on thesupport member are reduced for improved longevity.

It is noted that the ejector/mixer and the support member could be madeby additive manufacturing processes, such as direct metal lasersintering. Therefore, the ejector/mixer and the support member could bemade monolithically.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, the invention may be used with various types of gas turbineengines where cool and hot gases may simultaneously be in contact withthe machinery involved. Still other modifications which fall within thescope of the present invention will be apparent to those skilled in theart, in light of a review of this disclosure, and such modifications areintended to fall within the appended claims.

1. A gas turbine engine having an engine casing enclosing a compressorsection, a combustor and a turbine section defining a main gas pathserially extending therethrough, and comprising: an exhaust conedisposed downstream of the turbine section; an ejector/mixercantilevered from an aft end of the engine casing, the ejector/mixer atleast partially surrounding the exhaust cone such as to define a portionof the main gas path between an outer surface of the exhaust cone andthe ejector/mixer; the ejector/mixer having a plurality ofcircumferentially distributed lobes; and a support member connected toat least a number of the lobes; each of the at least number of lobesformed with a trough presenting a joint surface; the support memberhaving corresponding joint surfaces matingly cooperating with the shapeof the corresponding joint surface of the lobes.
 2. The gas turbineengine according to claim 1, wherein the trough has a convex bightradially inward thereof, wherein the joint surface of the lobes is aconvex joint surface, and wherein the joint surfaces of the supportmember have a concave profile configured to embrace the convex jointsurface of the lobes.
 3. The gas turbine engine according to claim 2,wherein the support member has an annular blade concentric with thelongitudinal axis of the engine and having the concave joint surfacesspaced apart to coincide with corresponding convex joint surfaces ofrespective lobes.
 4. The gas turbine engine according to claim 3,wherein the convex joint surface of each lobe is arcuate and the concavejoint surfaces of the annular blade are also arcuate to mate with theconvex joint surface of a corresponding lobe.
 5. The gas turbine engineaccording to claim 3, wherein the annular blade is disposed within themain gas path.
 6. The gas turbine engine according to claim 5, whereinthe annular blade is a circumferentially continuous one-piece metallicstrip.
 7. The gas turbine engine as defined in claim 5, wherein theannular blade is made up of blade segments wherein each segment has alength corresponding to the distance between the centerlines of twoadjacent lobes and each end has a partial concave arcuate surfaceadapted to mate with a portion of the convex joint surface of acorresponding lobe.
 8. The gas turbine engine as defined in claim 5,wherein the engine is a turbo-shaft engine and the lobes are configuredto induce cool air from the exterior of the engine casing to channelwithin the lobes.
 9. The gas turbine engine as defined in claim 5,wherein the engine is a turbofan engine and the inwardly extending lobesare part of a series of radially and radially outwardly alternatinglobes.
 10. An exhaust ejector/mixer for a gas turbine engine, theexhaust ejector/mixer comprising: an annular wall having an upstream endadapted to be fastened to an engine case and a downstream end forming aplurality of circumferentially distributed lobes; and a support memberdisposed towards the downstream end of the annular wall andinterconnecting at least a number of the lobes, each of the at leastnumber of lobes formed with a trough presenting a joint surface; thesupport member having corresponding joint surfaces profiled to mate withthe joint surfaces of the at least a number of lobes.
 11. The exhaustejector/mixer as defined in claim 10, wherein each trough has a convexbight radially inward thereof, the joint surface of the lobes beingprovided at said convex bight, the joint surfaces of the support memberhaving a concave profile to the mate with the joint surfaces of the atleast a number of lobes.
 12. The exhaust ejector/mixer as defined inclaim 11, wherein the lobes extend radially inwardly downstream relativeto the annular wall and the support member includes an annular bladethat has circumferentially spaced apart concave joint surfaces, spacedapart to coincide with the joint surfaces of the respective lobes. 13.The exhaust ejector/mixer as defined in claim 12, wherein the blade ismade up of blade segments with each segment having a lengthcorresponding to the distance between the centerlines of two adjacentlobes and each end has a partial concave surface adapted to mate with aportion of the joint surface of a corresponding lobe.
 14. The exhaustejector/mixer as defined in claim 12, wherein the annular blade is acontinuous one-piece sheet metal strip.
 15. The exhaust ejector/mixer asdefined in claim 12, wherein the joint surfaces of the lobes and theconcave joint surfaces of the support member are mating arcuatesurfaces.
 16. The exhaust ejector/mixer as defined in claim 12, whereinthe material of the blade and the annular wall are compatible for beingbonded together.
 17. The exhaust ejector/mixer as defined in claim 16,wherein the material of the blade and annular wall is sheet metal.